The present invention relates to inkjet ink compositions, which have good freeze-thaw stability as a result of the presence of a cryoprotectant component in the ink composition.
It is well known that many water-based particulate systems lack cryostability, i.e. show instability to a freeze-thaw cycle or cycles. Many dairy products, pharmaceutical emulsions, and water-based paints separate into two layers or show particle aggregation after a single freeze-thaw cycle. The reason for the instability is thought to be the formation of ice crystals, which tend to push emulsion or suspension particles together. For xe2x80x9chardxe2x80x9d suspension particles, such as pigments in paints, this results in the formation of irreversible clumps, so that increasing temperature does not resuspend them. In the gravity field, these clumps quickly settle. For xe2x80x9csoftxe2x80x9d particles, such as emulsions and vesicles (liposomes), ice crystals can cause irreversible coarsening of the system because of the liquid film breakage.
Suspensions of particles in the form of lipid bilayer vesicles or liposomes, as well as oil-in-water emulsions, in an aqueous vehicle have been studied in the pharmaceutical and/or biochemical context. Freeze-thaw experiments have shown that the presence of glycerol, dimethylsulfoxide (DMSO), certain sugars and certain amino acids confer a cryoprotectant effect on the lipid layers in the suspensions. See McDonald and McDonald, Liposome Technology, Vol. 1, pp. 209-227, 1993, CRC Press, Inc.; Strauss et al., Biochimica et Biophysica Acta 858 (1986) 169-180, Elsevier Science Publishers; Higgins et al., J. Pharm. Pharmacol. 1986, 38:259-263; Saito et al., Journal of Colloid and Interface Science 219: (1)129-134, Nov. 1, 1999.
Spinelli disclosed treating the problem of freeze-thaw instability in aqueous ink-jet inks with a polymer binder additive. See Spinelli in Adv. Mater. 1998, vol. 10, pp. 1215-1218. Spinelli also disclosed different acrylic block copolymers for use in pigmented inks for the purpose improving freeze-thaw instability in the inks. It appears that none of the additives disclosed by Spinelli effect more than limited improvement in cryostability.
Previously, polyols, such as glycerol, as well as sugars and/or amino acids have been used in aqueous ink-jet inks but have never been specifically used with the purpose of affecting the cryostability of the ink particulates.
Thus, Bermel and Burger (D. Bermel and D.E. Burger, xe2x80x9cParticle size effects in pigmented ink jet inksxe2x80x9d, J. Imaging Sc., Tech., V. 43 (1999) 320-324 disclosed several color pigmented inks in which the ink vehicle contains 7-12% glycerol. They specifically studied the freeze-thaw stability of the inks and found acceptable results for some dispersions. There was no discussion in the article of the role of glycerol (that is, the effect was not attributed to the presence of glycerol). The main objective was to show the particle size effect on the freeze-thaw stability.
Looman disclosed that acids containing a basic functional group help to alleviate bleed in pigmented ink jet inks (U.S. Pat. No. 5,679,143 assigned to HP). Specifically, Looman showed that when inks have amino acid additives such as beta-alanine, 4-aminobutyric acid, DL-alanine, glycine, threonine, sarcosine, diiodo-L-tyrosine, L-glutamic acid, L-histidine, hydroxy-L-proline, DL-isoleucine, DL-deucine, L-lysine, DL-methionine, DL-phenylalanine, L-proline, DL-serine, L-tryptophan, L-tyrosine, 6-aminocaproic acid, and DL-valine, that bleed control and pH adjustment are achieved. No mention is made of the effect of amino acids on freeze-thaw instability.
Gundlach et al. disclosed that the use of betaine zwitterionic base compositions as ink additives (U.S. Pat. No. 5,540,765, assigned to Xerox). In a related disclosure Gundlach et al. disclosed ink compositions with vesicles containing betaine (U.S. Pat. No. 5,772,743, assigned to Xerox). No connection was made between these compositions and freeze-thaw instability in either of these disclosures.
Yatake disclosed sugars as additives in ink-jet inks (U.S. Pat. No. 6,004,389, assigned to Seiko Epson). The disclosed benefits of these additives have nothing to do with freeze-thaw instability. Rather, it is taught that the addition of saccharide can effectively prevent clogging of the nozzle in the ink jet recording head.
The present invention relates to a method of using a cryoprotectant to improve freeze-thaw ability in an ink-jet ink composition comprising adding cryoprotectant to an ink-jet ink composition.